(1) Field of the Invention
The present invention relates to a facsimile apparatus provided with a printing head having a low line density.
(2) Description of the Related Art
A typical facsimile of thermal printing type comprises a thermal head having a line density of eight lines per millimeter. Since the facsimile of this type is capable of printing an image in high density, it can be used for receiving minute images such as drawings. Therefore, it has been widely used for business use.
On the other hand, in the facsimile transmission system, there are two transmission modes: a fine mode; and a standard mode. The fine mode is a mode in which a transmitting side transmits image data for every line, and the receiving side prints the received image data for every line. In the standard mode, the image data on one line is transmitted for two lines, and in the receiving side, the same received image data is printed on the first line and the second line. Therefor, although the standard mode has an advantage that the data transmitting time can be reduced by half compared to the fine mode, it has a disadvantage in terms of deterioration in image quality.
Recently, facsimiles have been coming into wide domestic use. For domestic use, a high density thermal head is needless since the images to be facsimiled are handwritten letters or characters in most cases. The high density thermal head requires a large number of driver circuits, causing the overall cost to become high. Therefore, a facsimile for domestic use is generally provided with a low density thermal head.
In such a facsimile for domestic use provided with a low density thermal head having line density of 4 lines per millimeter for example, image data for two adjacent dots in the main scanning direction (in the horizontal direction) of the received image data transmitted corresponding to the high line density of 8 lines per millimeter is converted into image data for one dot.
If the above-described conversion is performed for the fine mode, the resolution is reduced by half compared to that obtained by using the thermal head having line density of 8 lines per millimeter. It does not matter for domestic use. However, if the above conversion is performed for the standard mode, the resolution of the image is further reduced to a quarter, therefore, there arises a problem that a step-like notched shape peculiar to a digital image transmission system appears.